Steel ingots produced in steel mills are placed in a soaking pit furnace for heating the ingots to a temperature of about 2400.degree. F. The heated ingots are soaked at that temperature to uniformly heat them throughout until they are malleable enough to be rolled into sheet steel. In a commonly used soaking pit having a prior art burner, it presently takes approximately 2 to 4 hours to heat a steel ingot to a temperature of about 2400.degree. F. and another 4 hours or so to soak the ingot to its malleable condition. U.S. Pat. No. 2,480,255 to Mortson et al illustrates such a conventional burner for bottom-fired soaking pit furnaces. That burner includes an upright gas pipe disposed centrally in a relatively wide airflow channel which surrounds the gas pipe. Air flows upwardly through the airflow channel and mixes with the gas flowing from the pipe. The burner produces a yellow flame, indicating incomplete combustion. The incomplete combustion causes excessive oxide scale buildup on the surface of the steel ingots. The scale acts as a heat insulator which increases the time and energy required to heat up and soak the steel ingots. Moreover, the scale buildup on the ingots reduces the weight of high-grade steel production per ingot. The layer of oxide scale is removed from the ingots after they are soaked and is used in less profitable lower grade steel.
The present invention provides a burner for soaking pit furnaces which produces a continuous clean burning blue flame during use. By avoiding incomplete combustion, the burner of this invention reduces scale buildup on the surface of the ingots. This results in greater production of more profitable higher grade steel per ingot. The flame produced by the burner of this invention also burns hotter, which reduces the amount of time required for the ingots to reach their soaking temperature and to soak at that temperature. The hotter flame also provides a corresponding energy saving, because the amount of gas consumption required to heat each ingot is reduced. Inasmuch as scale buildup is reduced (the scale can act as an insulator), the amount of heat transferred to the ingots by the burner of this invention is increased, which provides an additional saving in heating and soaking time. By reducing soaking time, production of steel ingots can be increased for a given fuel cost. It is estimated that a typical steel mill using the burner of this invention can save several million dollars in production costs per year, when compared with the burners now in use in steel mills in this country.
Further, by avoiding incomplete combustion in the soaking pits, air pollution also is reduced; and the useful life of the soaking pit, burner, and furnace structure is extended.
My previous patent application, Ser. No. 850,235, discloses such a burner for soaking pits in which a continuous, clean-burning blue flame is produced. There is a need to ensure that the flame is constantly maintained adjacent the top of the burner, i.e., without a tendency to blow out or to migrate into the interior of the burner. There is also a need to maximize the amount of surrounding air mixed with the gaseous fuel to avoid incomplete combustion, while, at the same time, producing a more concentrated blue flame.